Two decades ago, the only known planetary system started at Mercury and ended at Pluto.

That's no longer the case, even minus Pluto. Astronomers have now found hundreds of planets orbiting hundreds of stars. And NASA's Kepler spacecraft has just added more than two dozen new exoplanets to the list.

Kepler keeps watch on a patch of more than 150,000 stars. It looks for stars that dim every so often as a planet passes across a star's face and blocks just a tiny fraction of starlight.

All 26 planets orbit closer to their respective host stars than Venus orbits the sun. So they're all expected to be too hot for life. But in the coming years Kepler should be able to identify stars that host Earth-like planets in temperate, potentially habitable orbits. In other words, planetary systems more like our own.

Scientific American is part of Springer Nature, which owns or has commercial relations with thousands of scientific publications (many of them can be found at www.springernature.com/us). Scientific American maintains a strict policy of editorial independence in reporting developments in science to our readers.